The present invention relates to plasma processing apparatuses and, more particularly, to a plasma processing apparatus for applying a process using plasma to a substrate to be processed such as a semiconductor wafer placed on a placement table in a vacuum process chamber.
In a manufacturing process of semiconductor devices, plasma is used so as to promote ionization or chemical reaction of process gases in various processes such as etching, CVD or sputtering. Generally, in a processing apparatus using a plasma, a placement table is installed in a hermetically sealed processing chamber so as to place a semiconductor wafer on the placement table to apply a process to the semiconductor wafer.
FIG. 1 is an illustration showing a structure of a conventional typical plasma processing apparatus. In the plasma processing apparatus, a placement table 204 is installed in the center of a process chamber 200, which is a vacuum chamber, via a support member 202. The semiconductor wafer W as a substrate to be processed is placed on a placement surface 204a of the placement table 204, which is formed in a disc-like shape.
The replacement table 204 is provided with an electrostatic attracting (chucking) function so as to attracts and retain the semiconductor wafer W by an electrostatic force. In this processing apparatus, an upper portion of at least the placement surface 204a of the placement table 204 is constituted by an insulating material, and an electrode 206 is provided therein. An appropriate voltage is applied to the electrode 206 from a direct current power source 208 provided outside the process chamber 200 so as to have the placement surface 204a attract and retain the semiconductor wafer W by an electrostatic force.
In the process chamber 200, a plasma P is generated above the placement table 204 by an appropriate method, and is lead near the surface of the semiconductor wafer W. At the same time, a predetermined process gas is introduced into the process chamber 200. The molecules of the introduced process gas are excited by the plasma P, thereby promoting fine processing such as a film deposition or an etching.
Ions and electrons in the plasma P can be incident on the surface of the wafer W in a vertical direction by applying a high-frequency bias voltage to the electrode 206 of the placement table 204. Thereby, directionality (anisotropy) can be provided to a fine processing by the plasma processing, which improves an accuracy of processing. In order to apply the high-frequency bias voltage, a normally 23.5 MHz high-frequency power source 210 is provided outside the process chamber 200.
The placement table 204 is installed, via an O-ring, on the support member 202, which is formed in a disc-like or cylindrical shape. A gap (space) 214 formed inside the O-ring 212 is separated from the depressurized process space in the process chamber 200. A power supply line and the like connected to the placement table 204 from outside extend through a through hole (not shown in the figure) formed in the support member 202 and the gap 214.
The support member 202 is a block made of a material having a high heat-conductivity such as aluminum, and has a coolant passage 202a therein. A coolant (for example, water) of a predetermined temperature (for example, 25xc2x0 C.) is supplied to the coolant passage 202a via a pipe (not shown in the figure) from a cooling apparatus (not shown in the figure) provided outside the process chamber 200. Thereby, the entire support member 202 is maintained at a predetermined temperature.
A heat of plasma transmitted to the placement table 204 via the semiconductor wafer W transmitted to the support member 202 from the placement table 204 via the gap 214. Then, the heat of plasma is absorbed by the coolant flowing through the coolant passage 202a formed in the support member 202, and is released to outside the chamber by the cooling apparatus. By this heat releasing mechanism, the temperature of the placement table 204 is maintained at a predetermined setting temperature (normally, equal to or lower than 200xc2x0 C.).
The reason for maintaining the setting temperature at a temperature equal to or lower than 200xc2x0 C. is that the O-ring 212 is in contact with a back surface of the placement table 204. That is, the O-ring 212 is formed by an elastic resin and a heat resistant temperature thereof is about 200xc2x0 C. at maximum.
Maintaining the setting temperature of the placement table 204 at a temperature equal to or lower than 200xc2x0 C. causes a large temperature difference between the placement table 204 and the semiconductor wafer W. In a general plasma process, a temperature of the wafer W is 400xc2x0 C., and, thus, it is necessary to provide a temperature difference of about 200xc2x0 C. between the two. The temperature difference is provided by contacting surfaces of the two and a thermal resistance of a space between the two.
It should be noted that a resistance heating element (not shown in the figure) may be provided inside the placement table 204, and an electrical control of an amount of heat generated by the resistance heating element is performed according to a temperature feedback function (not shown in the figure).
In the above-mentioned plasma process chamber, the temperature of the placement table 204 can be maintained at the setting temperature with a considerably high accuracy by the cooling by the support member 202 and the temperature control by heating by the equipped resistance heating element.
However, the with respect to the temperature of the wafer W which is an object whose temperature is to be controlled, it is difficult to compensate for with a fine thermal response in consideration of a temperature change caused by fluctuation in the plasma density and variation in a quality between individual wafers since the temperature difference between the semiconductor wafer W and the placement table 204. That is, it is difficult to maintain the temperature of the wafer W at a stable and uniform temperature.
Additionally, when starting the plasma processing, it is necessary to raise the temperature of the semiconductor wafer W to a temperature (setting temperature), at which the process can be started, after the semiconductor wafer W is placed on the placement table 204. This period is referred as a preheat time. If the temperature difference between the semiconductor wafer W and the placement table 204 is large as mentioned above, it is difficult to enhance the throughput since the preheat time is increased.
It is a general object of the present invention to provide an improved and useful plasma processing apparatus in which the above-mentioned problems.
A more specific object of the present invention is to provide a plasma processing apparatus which can obtain high throughput by reducing a preheat time from placement of a substrate to be processed on a placement table until the process is started.
In order to achieve the above-mentioned objects, there is provided according to the present invention a plasma processing apparatus for performing a process using a plasma with respect to a substrate to be processed within a depressurized process chamber, comprising:
a placement table, provided in said process chamber, having a placement surface for placing said substrate to be processed thereon and a back surface opposite to the placement surface; and
a support member supporting said placement table,
characterized in that said support member is provided between said placement table and a wall of said process chamber; said support member defines a space, which is separated from a process space of said process chamber, by being airtightly connected to said placement table and being airtightly connected to said process chamber; and said support member separates a connection part between said support member and the wall of said process chamber from said placement table by a predetermined distance so as to provide a predetermined thermal resistance between said placement table and said connection part.
According to the above-mentioned invention, since a predetermined thermal resistance is provided between said placement table and said connection part provided between the wall of the process chamber and the support member. Accordingly, the temperature of the connection part can be maintained at a low temperature while the placement table is maintained at the process temperature. Accordingly, connection part between the support member and the wall of the process chamber can be maintained to be equal to or smaller than a heat resistant temperature of rubber or plastics. That is, the connection part between the wall of the process chamber and the support member can be constituted by a seal member formed by rubber or plastics in an airtight manner.
Additionally, in the plasma processing apparatus according to the present invention, an elastic member for airtight connection may be provided to the connection part between the support member and the wall (10b) of the process chamber, and the connection part may be cooled by a first cooling means. By cooling the connection part by the first cooling means, an inexpensive seal member such as an O-ring or the like can be used as an elastic member for sealing.
Additionally, in the plasma processing apparatus according to the present invention, a second cooling means may be provided in the space separated by the support member so as to cool the placement table. By directly cooling the placement table by the second cooling means, the temperature of the placement table can be accurately and rapidly controlled.
Other objects, features and advantages of the resent invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.